Ultrastructure and immunohistochemical identification of the extracellular matrix of the chinchilla cochlea

Molecular differences between neonatal and adult stria vascularis from organotypic explants and transcriptomics

Summary

The stria vascularis (SV), part of the blood-labyrinth barrier, is an essential component of the inner ear that regulates the ionic environment required for hearing. SV degeneration disrupts cochlear homeostasis, leading to irreversible hearing loss, yet a comprehensive understanding of the SV, and consequently therapeutic availability for SV degeneration, is lacking. We developed a whole-tissue explant model from neonatal and adult mice to create a robust platform for SV research. We validated our model by demonstrating that the proliferative behaviour of the SV in vitro mimics SV in vivo, providing a representative model and advancing high-throughput SV research. We also provided evidence for pharmacological intervention in our system by investigating the role of Wnt/β-catenin signaling in SV proliferation. Finally, we performed single-cell RNA sequencing from in vivo neonatal and adult mouse SV and revealed key genes and pathways that may play a role in SV proliferation and maintenance. Together, our results contribute new insights into investigating biological solutions for SV-associated hearing loss.

Significance

Hearing loss impairs our ability to communicate with people and interact with our environment. This can lead to social isolation, depression, cognitive deficits, and dementia. Inner ear degeneration is a primary cause of hearing loss, and our study provides an in depth look at one of the major sites of inner ear degeneration: the stria vascularis. The stria vascularis and associated blood-labyrinth barrier maintain the functional integrity of the auditory system, yet it is relatively understudied. By developing a new in vitro model for the young and adult stria vascularis and using single cell RNA sequencing, our study provides a novel approach to studying this tissue, contributing new insights and widespread implications for auditory neuroscience and regenerative medicine.

Highlights

- We established an organotypic explant system of the neonatal and adult stria vascularis with an intact blood-labyrinth barrier. - Proliferation of the stria vascularis decreases with age in vitro , modelling its proliferative behaviour in vivo . - Pharmacological studies using our in vitro SV model open possibilities for testing injury paradigms and therapeutic interventions. - Inhibition of Wnt signalling decreases proliferation in neonatal stria vascularis.- We identified key genes and transcription factors unique to developing and mature SV cell types using single cell RNA sequencing.

The cochlear matrisome: Importance in hearing and deafness

The extracellular matrix (ECM) consists in a complex meshwork of collagens, glycoproteins, and proteoglycans, which serves a scaffolding function and provides viscoelastic properties to the tissues. ECM acts as a biomechanical support, and actively participates in cell signaling to induce tissular changes in response to environmental forces and soluble cues. Given the remarkable complexity of the inner ear architecture, its exquisite structure-function relationship, and the importance of vibration-induced stimulation of its sensory cells, ECM is instrumental to hearing. Many factors of the matrisome are involved in cochlea development, function and maintenance, as evidenced by the variety of ECM proteins associated with hereditary deafness. This review describes the structural and functional ECM components in the auditory organ and how they are modulated over time and following injury.

Visualizing Collagen Fibrils in the Cochlea's Tectorial and Basilar Membranes Using a Fluorescently Labeled Collagen-Binding Protein Fragment

PURPOSE

A probe that binds to unfixed collagen fibrils was used to image the shapes and fibrous properties of the TM and BM. The probe (CNA35) is derived from the bacterial adhesion protein CNA. We present confocal images of hydrated gerbil TM, BM, and other cochlear structures stained with fluorescently labeled CNA35. A primary purpose of this article is to describe the use of the CNA35 collagen probe in the cochlea.

METHODS

Recombinant poly-histidine-tagged CNA35 was expressed in Escherichia coli, purified by cobalt-affinity chromatography, fluorescence labeled, and further purified by gel filtration chromatography. Cochleae from freshly harvested gerbil bullae were irrigated with and then incubated in CNA35 for periods ranging from 2 h - overnight. The cochleae were fixed, decalcified, and dissected. Isolated cochlear turns were imaged by confocal microscopy.

RESULTS

The CNA35 probe stained the BM and TM, and volumetric imaging revealed the shape of these structures and the collagen fibrils within them. The limbal zone of the TM stained intensely. In samples from the cochlear base, intense staining was detected on the side of the TM that faces hair cells. In the BM pectinate zone, staining was intense at the upper and lower boundaries. The BM arcuate zone was characterized by a prominent longitudinal collagenous structure. The spiral ligament, limbus and lamina stained for collagen, and within the spiral limbus the habenula perforata were outlined with intense staining.

CONCLUSION

The CNA35 probe provides a unique and useful view of collagenous structures in the cochlea.

Hearing Loss in Exfoliation Syndrome: Systematic Review and Meta-Analysis

OBJECTIVE

To determine if exfoliation syndrome (XFS) is associated with hearing loss (HL) or vestibular dysfunction.

DATA SOURCES

PubMed, Scopus, CINAHL, and Cochrane Library through April 1, 2022.

REVIEW METHODS

Two reviewers independently screened abstracts, selected articles for inclusion, and extracted data. Studies included for qualitative analysis conducted audiometric, tympanometric, or vestibular evaluations on all subjects.

RESULTS

Twenty-one publications (1148 patients with XFS and 1212 controls) were included in the systematic review, and 16 publications (968 patients with XFS and 1147 controls) in the meta-analysis. Greater severity of HL was seen for patients with XFS compared to controls across all frequencies (odds ratio [OR] 8.8 [7.3-10.2]). Patients with XFS were more likely to have moderate to profound sensorineural HL (OR 1.8 [1.3-2.5]), and less likely to have none to mild HL (OR 0.34 [0.17-0.67]) or no HL (OR 0.37 [0.28-0.50]). Three studies found patients with XFS had lower tympanometric peaks. Two studies found that abnormal vestibular testing results could be more common for patients with XFS.

CONCLUSIONS

HL is associated with XFS. A sensorineural component to HL is confirmed, and mixed HL is possible. Given the high prevalence and infrequent diagnosis of XFS, the authors hypothesize that the current understandings of presbycusis might be improved by further investigation in XFS. Laryngoscope, 2022.

Targeted Deletion of Loxl3 by Col2a1-Cre Leads to Progressive Hearing Loss

Collagens are major constituents of the extracellular matrix (ECM) that play an essential role in the structure of the inner ear and provide elasticity and rigidity when the signals of sound are received and transformed into electrical signals. LOXL3 is a member of the lysyl oxidase (LOX) family that are copper-dependent amine oxidases, generating covalent cross-links to stabilize polymeric elastin and collagen fibers in the ECM. Biallelic missense variant of LOXL3 was found in Stickler syndrome with mild conductive hearing loss. However, available information regarding the specific roles of LOXL3 in auditory function is limited. In this study, we showed that the Col2a1-Cre-mediated ablation of Loxl3 in the inner ear can cause progressive hearing loss, degeneration of hair cells and secondary degeneration of spiral ganglion neurons. The abnormal distribution of type II collagen in the spiral ligament and increased inflammatory responses were also found in Col2a1–Loxl3^–/– mice. Amino oxidase activity exerts an effect on collagen; thus, Loxl3 deficiency was expected to result in the instability of collagen in the spiral ligament and the basilar membrane, which may interfere with the mechanical properties of the organ of Corti and induce the inflammatory responses that are responsible for the hearing loss. Overall, our findings suggest that Loxl3 may play an essential role in maintaining hearing function.

Postnatal structural development of mammalian Basilar Membrane provides anatomical basis for the maturation of tonotopic maps and frequency tuning

The basilar membrane (BM) of the mammalian cochlea constitutes a spiraling acellular ribbon that is intimately attached to the organ of Corti. Its graded stiffness, increasing from apex to the base of the cochlea provides the mechanical basis for sound frequency analysis. Despite its central role in auditory signal transduction, virtually nothing is known about the BM's structural development. Using polarized light microscopy, the present study characterized the architectural transformations of freshly dissected BM at time points during postnatal development and maturation. The results indicate that the BM structural elements increase progressively in size, becoming radially aligned and more tightly packed with maturation and reach the adult structural signature by postnatal day 20 (P20). The findings provide insight into structural details and developmental changes of the mammalian BM, suggesting that BM is a dynamic structure that changes throughout the life of an animal.

On the Role of Fibrocytes and the Extracellular Matrix in the Physiology and Pathophysiology of the Spiral Ligament

The spiral ligament in the cochlea has been suggested to play a significant role in the pathophysiology of different etiologies of strial hearing loss. Spiral ligament fibrocytes (SLFs), the main cell type in the lateral wall, are crucial in maintaining the endocochlear potential and regulating blood flow. SLF dysfunction can therefore cause cochlear dysfunction and thus hearing impairment. Recent studies have highlighted the role of SLFs in the immune response of the cochlea. In contrast to sensory cells in the inner ear, SLFs (more specifically type III fibrocytes) have also demonstrated the ability to regenerate after different types of trauma such as drug toxicity and noise. SLFs are responsible for producing proteins, such as collagen and cochlin, that create an adequate extracellular matrix to thrive in. Any dysfunction of SLFs or structural changes to the extracellular matrix can significantly impact hearing function. However, SLFs may prove useful in restoring hearing by their potential to regenerate cells in the spiral ligament.

Some Ototoxic Drugs Destroy Cochlear Support Cells Before Damaging Sensory Hair Cells

A wide variety of ototoxic drugs are capable of damaging the sensory hair cells in the mammalian cochlea resulting in permanent hearing loss. However, the toxic properties of these drugs suggest that some could potentially damage cochlear support cells as well. To test the hypothesis, we treated postnatal day three rat cochlear cultures with toxic doses of gentamicin, cisplatin, mefloquine, and cadmium. Gentamicin primarily destroyed the hair cells and disrupted the intercellular connection with the surrounding support cells. Gentamicin-induced hair cell death was initiated through the caspase-9 intrinsic apoptotic pathway followed by activation of downstream executioner caspase-3. In contrast, cisplatin, mefloquine, and cadmium initially damaged the support cells and only later damaged the hair cells. Support cell death was initiated through the caspase-8 extrinsic apoptotic pathway followed later by downstream activation of caspase-3. Cisplatin, mefloquine, and cadmium significantly reduced the expression of actin and laminin, in the extracellular matrix, leading to significant disarray of the sensory epithelium.

Synaptic coupling of inner ear sensory cells is controlled by brevican-based extracellular matrix baskets resembling perineuronal nets

Background

Perineuronal nets (PNNs) are specialized aggregations of extracellular matrix (ECM) molecules surrounding specific neurons in the central nervous system (CNS). PNNs are supposed to control synaptic transmission and are frequently associated with neurons firing at high rates, including principal neurons of auditory brainstem nuclei. The origin of high-frequency activity of auditory brainstem neurons is the indefatigable sound-driven transmitter release of inner hair cells (IHCs) in the cochlea.

Results

Here, we show that synaptic poles of IHCs are ensheathed by basket-like ECM complexes formed by the same molecules that constitute PNNs of neurons in the CNS, including brevican, aggreccan, neurocan, hyaluronan, and proteoglycan link proteins 1 and 4 and tenascin-R. Genetic deletion of brevican, one of the main components, resulted in a massive degradation of ECM baskets at IHCs, a significant impairment in spatial coupling of pre- and postsynaptic elements and mild impairment of hearing.

Conclusions

These ECM baskets potentially contribute to control of synaptic transmission at IHCs and might be functionally related to PNNs of neurons in the CNS.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0566-8) contains supplementary material, which is available to authorized users.

Scanning Electron Microscopic Examination of the Extracellular Matrix in the Decellularized Mouse and Human Cochlea

Decellularized tissues have been used to investigate the extracellular matrix (ECM) in a number of different tissues and species. Santi and Johnson JARO 14:3-15 (2013) first described the decellularized inner ear in the mouse, rat, and human using scanning thin-sheet laser imaging microscopy (sTSLIM). The purpose of the present investigation is to examine decellularized cochleas in the mouse and human at higher resolution using scanning electron microscopy (SEM). Fresh cochleas were harvested and decellularized using detergent extraction methods. Following decellularization, the ECM of the bone, basilar membrane, spiral limbus, and ligament remained, and all of the cells were removed from the cochlea. A number of similarities and differences in the ECM of the mouse and human were observed. A novel, spirally directed structure was present on the basilar membrane and is located at the border between Hensen and Boettcher cells. These septa-like structures formed a single row in the mouse and multiple rows in the human. The basal lamina of the stria vascularis capillaries was present and appeared thicker in the human compared with the mouse. In the mouse, numerous openings beneath the spiral prominence that previously housed the root processes of the external sulcus cells were observed but in the human there was only a single row of openings. These and other anatomical differences in the ECM between the mouse and human may reflect functional differences and/or be due to aging; however, decellularized cochleas provide a new way to examine the cochlear ECM and reveal new observations.

Where hearing starts: the development of the mammalian cochlea

The mammalian cochlea is a remarkable sensory organ, capable of perceiving sound over a range of 10(12) in pressure, and discriminating both infrasonic and ultrasonic frequencies in different species. The sensory hair cells of the mammalian cochlea are exquisitely sensitive, responding to atomic-level deflections at speeds on the order of tens of microseconds. The number and placement of hair cells are precisely determined during inner ear development, and a large number of developmental processes sculpt the shape, size and morphology of these cells along the length of the cochlear duct to make them optimally responsive to different sound frequencies. In this review, we briefly discuss the evolutionary origins of the mammalian cochlea, and then describe the successive developmental processes that lead to its induction, cell cycle exit, cellular patterning and the establishment of topologically distinct frequency responses along its length.

The expression pattern and inhibitory influence of Tenascin-C on the growth of spiral ganglion neurons suggest a regulatory role as boundary formation molecule in the postnatal mouse inner ear

Sensorineural hearing loss, as a consequence of acoustic trauma, aging, genetic defects or ototoxic drugs, is highly associated with irreversible damage of cochlear hair cells (HCs) and secondary degeneration of spiral ganglion (SG) cells. Cochlear implants (CIs), which bypass the lost HC function by direct electrical stimulation of the remaining auditory neurons, offer an effective therapy option. Several studies imply that components of the extracellular matrix (ECM) have a great impact on the adhesion and growth of spiral ganglion neurons (SGNs) during development. Based on these findings, ECM proteins might act as bioactive CI substrates to optimize the electrode-nerve interface and to improve efficacy of these implants. In the present study, we focused on the ECM glycoproteins Tenascin-C (TN-C), Laminin (LN), and Fibronectin (FN), which show a prominent expression along the growth route of SGNs and the niche around HCs during murine postnatal development in vivo. We compared their influence on adhesion, neurite length, and neurite number of SGNs in vitro. Moreover, we studied the expression of the chondroitin sulfate proteoglycan (CSPG) dermatan sulfate-dependent proteoglycan-1 (DSD-1-PG), an interaction partner of TN-C. In sum, our in vitro data suggest that TN-C acts as an anti-adhesive and inhibitory factor for the growth of SGNs. The DSD-1 carbohydrate epitope is specifically localized to HC stereocilia and SG fibers. Interestingly, TN-C and the DSD-1-PG exhibit a mutually exclusive expression pattern, with the exception of a very restricted region beneath the habenula perforata, where SG neurites grow through the basilar membrane (BM) toward the HCs. The complementary expression of TN-C, LN, FN, and the DSD-1 epitope suggests that TN-C may act as an important boundary formation molecule in the developing postnatal mouse inner ear, which makes it a promising candidate to regulate neurite outgrowth in the light of CIs.

Macromolecular organization and fine structure of the human basilar membrane - RELEVANCE for cochlear implantation

INTRODUCTION

Cochlear micromechanics and frequency tuning depend on the macromolecular organization of the basilar membrane (BM), which is still unclear in man. Novel techniques in cochlear implantation (CI) motivate further analyses of the BM.

MATERIALS AND METHODS

Normal cochleae from patients undergoing removal of life-threatening petro-clival meningioma and an autopsy specimen from a normal human were used. Laser-confocal microscopy, high resolution scanning (SEM) and transmission electron microscopy (TEM) were carried out in combination. In addition, one human temporal bone was decellularized and investigated by SEM.

RESULTS

The human BM consisted in four separate layers: (1) epithelial basement membrane positive for laminin-β2 and collagen IV, (2) BM "proper" composed of radial fibers expressing collagen II and XI, (3) layer of collagen IV and (4) tympanic covering layer (TCL) expressing collagen IV, fibronectin and integrin. BM thickness varied both radially and longitudinally (mean 0.55-1.16 μm). BM was thinnest near the OHC region and laterally.

CONCLUSIONS

There are several important similarities and differences between the morphology of the BM in humans and animals. Unlike in animals, it does not contain a distinct pars tecta (arcuate) and pectinata. Its width increases and thickness decreases as it travels apically in the cochlea. Findings show that the human BM is thinnest and probably most vibration-sensitive at the outer pillar feet/Deiter cells at the OHCs. The inner pillar and IHCs seem situated on a fairly rigid part of the BM. The gradient design of the BM suggests that its vulnerability increases apical wards when performing hearing preservation CI surgery.

The pre- and post-somatic segments of the human type I spiral ganglion neurons--structural and functional considerations related to cochlear implantation

Human auditory nerve afferents consist of two separate systems; one is represented by the large type I cells innervating the inner hair cells and the other one by the small type II cells innervating the outer hair cells. Type I spiral ganglion neurons (SGNs) constitute 96% of the afferent nerve population and, in contrast to other mammals, their soma and pre- and post-somatic segments are unmyelinated. Type II nerve soma and fibers are unmyelinated. Histopathology and clinical experience imply that human SGNs can persist electrically excitable without dendrites, thus lacking connection to the organ of Corti. The biological background to this phenomenon remains elusive. We analyzed the pre- and post-somatic segments of the type I human SGNs using immunohistochemistry and transmission electron microscopy (TEM) in normal and pathological conditions. These segments were found surrounded by non-myelinated Schwann cells (NMSCs) showing strong intracellular expression of laminin-β2/collagen IV. These cells also bordered the perikaryal entry zone and disclosed surface rugosities outlined by a folded basement membrane (BM) expressing laminin-β2 and collagen IV. It is presumed that human large SGNs are demarcated by three cell categories: (a) myelinated Schwann cells, (b) NMSCs and (c) satellite glial cells (SGCs). Their BMs express laminin-β2/collagen IV and reaches the BM of the sensory epithelium at the habenula perforata. We speculate that the NMSCs protect SGNs from further degeneration following dendrite loss. It may give further explanation why SGNs can persist as electrically excitable monopolar cells even after long-time deafness, a blessing for the deaf treated with cochlear implantation.

Expression and function of scleraxis in the developing auditory system

A study of genes expressed in the developing inner ear identified the bHLH transcription factor Scleraxis (Scx) in the developing cochlea. Previous work has demonstrated an essential role for Scx in the differentiation and development of tendons, ligaments and cells of chondrogenic lineage. Expression in the cochlea has been shown previously, however the functional role for Scx in the cochlea is unknown. Using a Scx-GFP reporter mouse line we examined the spatial and temporal patterns of Scx expression in the developing cochlea between embryonic day 13.5 and postnatal day 25. Embryonically, Scx is expressed broadly throughout the cochlear duct and surrounding mesenchyme and at postnatal ages becomes restricted to the inner hair cells and the interdental cells of the spiral limbus. Deletion of Scx results in hearing impairment indicated by elevated auditory brainstem response (ABR) thresholds and diminished distortion product otoacoustic emission (DPOAE) amplitudes, across a range of frequencies. No changes in either gross cochlear morphology or expression of the Scx target genes Col2A, Bmp4 or Sox9 were observed in Scx(-/-) mutants, suggesting that the auditory defects observed in these animals may be a result of unidentified Scx-dependent processes within the cochlea.

Inner ear supporting cells: rethinking the silent majority

Sensory epithelia of the inner ear contain two major cell types: hair cells and supporting cells. It has been clear for a long time that hair cells play critical roles in mechanoreception and synaptic transmission. In contrast, until recently the more abundant supporting cells were viewed as serving primarily structural and homeostatic functions. In this review, we discuss the growing information about the roles that supporting cells play in the development, function and maintenance of the inner ear, their activities in pathological states, their potential for hair cell regeneration, and the mechanisms underlying these processes.

Quantitative polarized light microscopy of unstained mammalian cochlear sections

Hearing loss is the most common sensory deficit in the world, and most frequently it originates in the inner ear. Yet, the inner ear has been difficult to access for diagnosis because of its small size, delicate nature, complex three-dimensional anatomy, and encasement in the densest bone in the body. Evolving optical methods are promising to afford cellular diagnosis of pathologic changes in the inner ear. To appropriately interpret results from these emerging technologies, it is important to characterize optical properties of cochlear tissues. Here, we focus on that characterization using quantitative polarized light microscopy (qPLM) applied to unstained cochlear sections of the mouse, a common animal model of human hearing loss. We find that the most birefringent cochlear materials are collagen fibrils and myelin. Retardance of the otic capsule, the spiral ligament, and the basilar membrane are substantially higher than that of other cochlear structures. Retardance of the spiral ligament and the basilar membrane decrease from the cochlear base to the apex, compared with the more uniform retardance of other structures. The intricate structural details revealed by qPLM of unstained cochlear sections ex vivo strongly motivate future application of polarization-sensitive optical coherence tomography to human cochlea in vivo.

Metalloproteinases and their associated genes contribute to the functional integrity and noise-induced damage in the cochlear sensory epithelium

Matrix metalloproteinases (MMPs) and their related gene products regulate essential cellular functions. An imbalance in MMPs has been implicated in various neurological disorders, including traumatic injuries. Here, we report a role for MMPs and their related gene products in the modulation of cochlear responses to acoustic trauma in rats. The normal cochlea was shown to be enriched in MMP enzymatic activity, and this activity was reduced in a time-dependent manner after traumatic noise injury. The analysis of gene expression by RNA sequencing and qRT-PCR revealed the differential expression of MMPs and their related genes between functionally specialized regions of the sensory epithelium. The expression of these genes was dynamically regulated between the acute and chronic phases of noise-induced hearing loss. Moreover, noise-induced expression changes in two endogenous MMP inhibitors, Timp1 and Timp2, in sensory cells were dependent on the stage of nuclear condensation, suggesting a specific role for MMP activity in sensory cell apoptosis. A short-term application of doxycycline, a broad-spectrum inhibitor of MMPs, before noise exposure reduced noise-induced hearing loss and sensory cell death. In contrast, a 7 d treatment compromised hearing sensitivity and potentiated noise-induced hearing loss. This detrimental effect of the long-term inhibition of MMPs on noise-induced hearing loss was further confirmed using targeted Mmp7 knock-out mice. Together, these observations suggest that MMPs and their related genes participate in the regulation of cochlear responses to acoustic overstimulation and that the modulation of MMP activity can serve as a novel therapeutic target for the reduction of noise-induced cochlear damage.

Prolyl 3-hydroxylase-1 null mice exhibit hearing impairment and abnormal morphology of the middle ear bone joints

Prolyl 3-hydroxylase1 (P3H1) is a collagen modifying enzyme which hydroxylates certain prolines in the Xaa position of conventional GlyXaaYaa triple helical sequence. Recent investigations have revealed that mutations in the LEPRE1 (gene encoding for P3H1) cause severe osteogenesis imperfecta (OI) in humans. Similarly LEPRE1 knockout mice display an OI-like phenotype. Significant hearing loss is a common problem for people with osteogenesis imperfecta. Here we report that hearing of the P3H1 null mice is substantially affected. Auditory brainstem responses (ABRs) of the P3H1 null mice show an average increase of 20-30 dB in auditory thresholds. Three dimensional reconstructions of the mutant middle ear bones by Micro-scale X-ray computed tomography (Micro-CT) demonstrate abnormal morphology of the incudostapedial and incudomalleal joints. We establish the LEPRE1 knockout mouse as a valuable model system to investigate the mechanism of hearing loss in recessive OI.

Cochlin expression in vestibular endorgans obtained from patients with Meniere's disease

The distribution of cochlin and its associated basement membrane proteins (collagen IV, collagen II, laminin-β2, and nidogen-1) were evaluated in the vestibular endorgans of subjects with Meniere's disease and compared with normal specimens. Cochlin mRNA expression in vestibular endorgans from Meniere's disease specimens was also investigated. Specimens were obtained from patients who had Meniere's disease and who were undergoing ablative labyrinthectomy. Control specimens were obtained both from autopsy specimens with documented normal audiovestibular function and from patients undergoing labyrinthectomy for acoustic neuroma excision. In the normal control specimens, cochlin immunoreactivity was found evenly distributed in the stroma of the cristae ampullaris and maculae of the utricle. In Meniere's specimens, cochlin immunoreactivity was markedly increased; this was associated with an increase in cochlin mRNA expression as shown by real-time reverse transcription with the polymerase chain reaction. Collagen IV and laminin-β2 immunoreactivity was significantly decreased in Meniere's specimens. Nidogen-1 and collagen II immunoreactivity was unchanged in Meniere's specimens when compared with normal samples. Cochlin upregulation has been implicated in the hereditary audiovestibulopathy, DFNA9. The increased expression of cochlin and decreased expression of collagen IV and laminin in Meniere's disease are suggestive that the overexpression of cochlin contributes to the dysfunctional inner ear homeostasis seen in this disease.

Decellularized ear tissues as scaffolds for stem cell differentiation

Permanent sensorineural hearing loss is a major medical problem and is due to the loss of hair cells and subsequently spiral ganglion neurons in the cochlea. Since these cells lack the capacity of renewal in mammals, their regeneration would be an optimal solution to reverse hearing loss. In other tissues, decellularized extracellular matrix (ECM) has been used as a mechanical and biochemical scaffold for the induction of stem and other cells toward a target tissue phenotype. Such induced cells have been used for tissue and organ transplants in preclinical animal and human clinical applications. This paper reports for the first time the decellularization of the cochlea and identification of remaining laminin and collagen type IV as a first step in preparing an ECM scaffold for directing stem cells toward an auditory lineage. Fresh ear tissues were removed from euthanized mice, a rat and a human and processed for decellularization using two different detergent extraction methods. Cochleas were imaged with scanning thin-sheet laser imaging microscopy (sTSLIM) and brightfield microscopy. Detergent treatment of fresh tissue removed all cells as evidenced by lack of H&E and DNA staining of the membranous labyrinth while preserving components of the ECM. The organ of Corti was completely removed, as were spiral ganglion neurons, which appeared as hollow sheaths and tubes of basal lamina (BL) material. Cells of the stria vascularis were removed and its only vestige left was its laterally linking network of capillary BL that appeared to "float" in the endolymphatic space. Laminin and type IV collagen were detected in the ECM after decellularization and were localized in vascular, neural and epithelial BL. Further work is necessary to attempt to seed neural and other stem cells into the decellularized ECM to hopefully induce differentiation and subsequent in vivo engraftment into damaged cochleas.

Quantification of collagen organization using fractal dimensions and Fourier transforms

Collagen fibers and fibrils that comprise tendons and ligaments are disrupted or damaged during injury. Fibrillogenesis during healing produces a matrix that is initially quite disorganized, but remodels over time to resemble, but not replicate, the original roughly parallel microstructure. Quantification of these changes is traditionally a laborious and subjective task. In this work we applied two automated techniques, fast Fourier transformation (FFT) and fractal dimension analysis (FA) to quantify the organization of collagen fibers or fibrils. Using multi-photon images of collagen fibers obtained from rat ligament we showed that for healing ligaments, FA differentiates more clearly between the different time-points during healing. Using scanning electron microscopy images of overstretched porcine flexor tendon, we showed that combining FFT and FA measures distinguishes the damaged and undamaged groups more clearly than either method separately.

Transcriptional changes in adhesion-related genes are site-specific during noise-induced cochlear pathogenesis

Cell-cell junctions and junctions between cells and extracellular matrix are essential for maintenance of the structural and functional integrity of the cochlea, and are also a major target of acoustic trauma. While morphological assessments have revealed adhesion dysfunction in noise-traumatized cochleae, the molecular mechanisms responsible for adhesion disruption are not clear. Here, we screened the transcriptional expression of 49 adhesion-related genes in normal rat cochleae and measured the expression changes in the early phases of cochlear pathogenesis after acoustic trauma. We found that genes from four adhesion families, including the immunoglobulin superfamily and the integrin, cadherin, and selectin families, are expressed in the normal cochlea. Exposure to an intense noise at 120dB sound pressure level (SPL) for 2h caused site-specific changes in expression levels in the apical and the basal sections of the sensory epithelium. Expression changes that occurred in the cochlear sensory epithelium were biphasic, with early upregulation at 2h post-noise exposure and subsequent downregulation at 1day post-exposure. Importantly, the altered expression level of seven genes (Sgce, Sell, Itga5, Itgal, Selp, Cntn1 and Col5a1) is related to the level of threshold shift of the auditory brainstem response (ABR), an index reflecting functional change in the cochlea. Notably, the genes showing expression changes exhibited diverse constitutive expression levels and belong to multiple adhesion gene families. The finding of expression changes in multiple families of adhesion genes in a temporal fashion (2h vs. 1day) and a spatial fashion (the apical and the basal sensory epithelia as well as the lateral wall tissue) suggests that acoustic overstimulation provokes a complex response in adhesion genes, which likely involves multiple adhesion-related signaling pathways.

Development of tonotopy in the auditory periphery

Acoustic frequency analysis plays an essential role in sound perception, communication and behavior. The auditory systems of most vertebrates that perceive sounds in air are organized based on the separation of complex sounds into component frequencies. This process begins at the level of the auditory sensory epithelium where specific frequencies are distributed along the tonotopic axis of the mammalian cochlea or the avian/reptilian basilar papilla (BP). Mechanical and electrical mechanisms mediate this process, but the relative contribution of each mechanism differs between species. Developmentally, structural and physiological specializations related to the formation of a tonotopic axis form gradually over an extended period of time. While some aspects of tonotopy are evident at early stages of auditory development, mature frequency discrimination is typically not achieved until after the onset of hearing. Despite the importance of tonotopic organization, the factors that specify unique positional identities along the cochlea or basilar papilla are unknown. However, recent studies of developing systems, including the inner ear provide some clues regarding the signalling pathways that may be instructive for the formation of a tonotopic axis.

Acoustic overstimulation modifies Mcl-1 expression in cochlear sensory epithelial cells

Acoustic overstimulation causes apoptotic cell death in the cochlea. This death process is mediated, in part, by the mitochondrial signaling pathway involving Bcl-2 family proteins. Myeloid cell leukemia sequence 1 (Mcl-l) is an antiapoptotic member of the Bcl-2 family. Its involvement in noise-induced hair cell death has not been characterized. Here we report the endogenous expression and the noise-induced expression of Mcl-1 in Sprague Dawley rat cochleae. In the sensory epithelia of normal cochleae, there is strong constitutive expression of Mcl-1 mRNA, with an expression level higher than that of many other Bcl-2 family genes. The Mcl-1 protein is preferentially expressed in outer hair cells. After exposure to a high level of continuous noise at 115-dB sound pressure level for 1 hr, Mcl-1 expression displays a time-dependent alteration, with up-regulation of Mcl-1 mRNA at 4 hr postexposure and protein up-regulation at 1 day postexposure. Western blot analysis reveals the up-regulated Mcl-1 as the full-length form of Mcl-1. Immunolabeling of the Mcl-1 protein reveals the early increase in Mcl-1 immunoreactivity in the nuclear region of the hair cells displaying apoptotic phenotypes and a subsequent increase in survival hair cells. These results suggest that Mcl-1 is involved in the regulation of hair cell pathogenesis resulting from acoustic stress, possibly by influencing the nuclear events of apoptosis.

Compliance profiles derived from a three-dimensional finite-element model of the basilar membrane

A finite-element analysis is used to explore the impact of elastic material properties, boundary conditions, and geometry, including coiling, on the spatial characteristics of the compliance of the unloaded basilar membrane (BM). It is assumed that the arcuate zone is isotropic and the pectinate zone orthotropic, and that the radial component of the effective Young's modulus in the pectinate zone decreases exponentially with distance from base to apex. The results concur with tonotopic characteristics of compliance and neural data. Moreover, whereas the maximum compliance in a radial profile is located close to the boundary between the two zones in the basal region, it shifts to the midpoint of the pectinate zone for the apical BM; the width of the profile also expands. This shift begins near the 1 kHz characteristic place for guinea pig and the 2.4 kHz place for gerbil. Shift and expansion are not observed for linear rather than exponential decrease of the radial component of Young's modulus. This spatial change of the compliance profile leads to the prediction that mechanical excitation in the apical region of the organ of Corti is different to that in the basal region.

Nanotopographical modification: a regulator of cellular function through focal adhesions

As materials technology and the field of biomedical engineering advances, the role of cellular mechanisms, in particular adhesive interactions with implantable devices, becomes more relevant in both research and clinical practice. A key tenet of medical device design has evolved from the exquisite ability of biological systems to respond to topographical features or chemical stimuli, a process that has led to the development of next-generation biomaterials for a wide variety of clinical disorders. In vitro studies have identified nanoscale features as potent modulators of cellular behavior through the onset of focal adhesion formation. The focus of this review is on the recent developments concerning the role of nanoscale structures on integrin-mediated adhesion and cellular function with an emphasis on the generation of medical constructs with regenerative applications.

FROM THE CLINICAL EDITOR

In this review, recent developments related to the role of nanoscale structures on integrin-mediated adhesion and cellular function is discussed, with an emphasis on regenerative applications.

Histopathological and ultrastructural analysis of vestibular endorgans in Meniere's disease reveals basement membrane pathology

BACKGROUND

We report the systematic analysis of the ultrastructural and cytological histopathology of vestibular endorgans acquired from labyrinthectomy in Meniere's disease.

METHODS

17 subjects with intractable Meniere's disease and ipsilateral non-serviceable hearing presenting to the Neurotology Clinic from 1997 to 2006 who chose ablative labyrinthectomy (average age = 62 years; range 29-83 years) participated. The average duration of symptoms prior to surgery was 7 years (range 1-20 years).

RESULTS

Nearly all vestibular endorgans demonstrated varying degrees of degeneration. A monolayer of epithelial cells occurred significantly more frequently in the horizontal cristae (12/13 = 92%) (p < 0.001), the superior cristae (5/5 = 100%) (p < 0.005), the posterior cristae (2/2) compared with the utricular maculae (4/17 = 24%). Basement membrane (BM) thickening was more common in all of the cristae ampullares (18 out of 20) than the utricular maculae. Although only four saccular maculae were obtained, 3 out of 4 exhibited BM thickening and monolayer degeneration. Monolayer degeneration was highly significantly correlated with the presence of BM thickening (p < 0.001). Other degenerative changes noted equally among the five vestibular endorgans which were not significantly correlated with BM thickening or monolayer degeneration included hair cell vacuolization and stereocilia loss, microvesicles in the supporting cells, and increased stromal intercellular spaces. Transmission electron microscopy demonstrated disorganization of the BM collagen-like fibrils, and normal ultrastructural morphology of the nerve terminals and myelinated fibers. Stromal fibroblasts and endothelial cells of stromal blood vessels demonstrated vacuolization, and stromal perivascular BMs were also thickened.

CONCLUSION

Systematic histopathological analysis of the vestibular endorgans from Meniere's disease demonstrated neuroepithelial degeneration which was highly correlated with an associated BM thickening. Other findings included hair cell and supporting cell microvessicles, increased intercellular clear spaces in the stroma, and endothelial cell vacuolization and stromal perivascular BM thickening.

Immunohistochemical distribution of basement membrane proteins in the human inner ear from older subjects

The immunolocalization of several basement membrane (BM) proteins was investigated in vestibular endorgans microdissected from temporal bones obtained from subjects with a documented normal auditory and vestibular function (n=5, average age=88 years old). Fluorescent immunostaining using antibodies directed at collagen IV alpha 2, nidogen-1, laminin-beta2, alpha-dystroglycan, and tenascin-C was applied to cryosections from human cochlea, cristae ampullares, utricular and saccular maculae. Collagen IV alpha 2, nidogen-1, and laminin-beta2 localized to all subepithelial cochlear BMs, Reissner's membrane, strial and spiral ligamental perineural and perivascular BMs, and the spiral limbus. Tenascin-C localized to the basilar membrane and the osseous spiral lamina. alpha-Dystroglycan localized to most cochlear BMs except those in the spiral ligament, basilar membrane and spiral limbus. Collagen IV, nidogen-1, and laminin-beta2 localized to the subepithelial BMs of the maculae and cristae ampullares, and the perineural and perivascular BMs within the underlying stroma. The BM underlying the transitional and dark cell region of the cristae ampullares also expressed collagen IV, nidogen-1, and laminin-beta2. Tenascin-C localized to the subepithelial BMs of the utricular maculae and cristae ampullares, and to calyx-like profiles throughout the vestibular epithelium, but not to the perineural and perivascular BMs. alpha-Dystroglycan colocalized with aquaporin-4 in the basal vestibular supporting cell, and was also expressed in the subepithelial BMs, as well as perivascular and perineural BMs. This study provides the first comprehensive immunolocalization of these ECM proteins in the human inner ear. The validity of the rodent models for inner ear disorders secondary to BM pathologies was confirmed as there is a high degree of conservation of expression of these proteins in the human inner ear. This information is critical to begin to unravel the role that BMs may play in human inner ear physiology and audiovestibular pathologies.

Adenoviral vectors for improved gene delivery to the inner ear

An important requirement for gene therapy in the inner ear is to achieve efficient gene delivery without damaging residual inner ear function. This can be achieved by delivering a high concentration of vector in a minimal volume. Adenovectors are well suited to meet these requirements since high quality concentrated vector with a high capacity for a gene payload can be produced. To reduce the number of vector particles and volume of delivery to the inner ear, we tested vectors with enhancements in cell binding and cell entry properties. We compared delivery of a marker gene to the inner ear using two different advanced generation serotype 5 adenovector designs. The first adenovector tested, AdRGD, has a restricted tropism of entry into cells. AdRGD is an Ad5 capsid vector with an arg-gly-asp (RGD) motif built into the adenovector fiber that has also been modified to abolish the fiber-CAR and penton-integrin interactions that provide the normal well characterized two-step entry pathway for adenovirus. The AdRGD vector has enhanced binding to alphanu integrins. The second vector, AdF2K, contains 7 lysine residues within the fiber knob and has been shown to have expanded tropism for cells in vitro and in vivo. AdF2K maintains its normal CAR and integrin receptors interactions and has an additional mechanism of entry via its ability to interact with heparan sulfate. Both vectors demonstrated effective delivery to the inner ear and more uniform labeling of the inner ear sensory epithelia than native capsid vector, when tested in vivo. Analysis of expression efficiency using quantitative PCR was tested in vitro on cultured macular organs and demonstrated that vector delivery with the AdF2K vector design yielded optimal delivery. The present study demonstrates that retargeting strategies can improve delivery to the inner ear.

Environmental Micropatterning for the Study of Spiral Ganglion Neurite Guidance

The projection of neuronal processes is guided by a variety of soluble and insoluble factors, which are sensed by a fiber's growth cone. It is the differential distribution of such guidance cues that determine the direction in which neurites grow. The growth cone senses these cues on a fine scale, using extensible filopodia that range from a few to tens of mum in length. In order to study the effects of guidance cues on spiral ganglion (SG) neurites, we have used methods for distributing both soluble and insoluble cues on a scale appropriate for sensing by growth filopodia. The scale of these methods are at the micro, rather than nano, level to match the sensing range of the growth cone. Microfluidics and transfected cells were used to spatially localize tropic factors within the fluid environment of extending neurites. Micro-patterning was used to present neurites with stripes of insoluble factors. The results indicate that differentially distributed permissive, repulsive and stop signals can control the projection of SG neurites. Implications for future micro-patterning studies, for SG development and for the growth of deafferented SG dendrites toward a cochlear implant are discussed.

Expression of Cochlin in the Vestibular Organ of Rats

The COCH gene mutated in autosomal dominant sensorineural deafness (DFNA9) encodes cochlin, a major constituent of the inner ear extracellular matrix. Cochlin constitutes 70% of the inner ear protein and cochlin isoforms can be classified into three subgroups, p63s, p44s and p40s. Symptoms of some DFNA9 patients are consistent with those of Ménière's disease. Here, we report the expression of cochlin in the vestibular organ of rats using isoform-specific antibodies that recognize all three isoforms. Cochlin is highly expressed in the stromata of the maculae of otolithic organs and cristae of semicircular canals, and in the channels in the bony labyrinth that transmit the dendritic innervation to the cristae and maculae. Cochlin cannot be detected in the sensory cells, dark cells, nor in the acellular structures, otolithic membrane or in the cupula. These findings support the theory that deposition of acidophilic substance in the inner ear caused by mutation of cochlin can induce a secondary retrograde dendritic degeneration of the vestibular nerves.

Abnormal basement membrane in the inner ear and the kidney of the Mpv17-/- mouse strain: ultrastructural and immunohistochemical investigations

The loss of the function of the peroxisomal Mpv17-protein and associated imbalanced radical oxygen species (ROS) homeostasis leads to an early onset of focal segmental glomerulosclerosis and sensorineural deafness associated with severe degeneration of cochlear structures. An excessive enlargement of basal laminae of the stria vascularis capillaries and glomeruli indicates numerous changes in their molecular composition. The basement membrane (BM) of the glomeruli and the stria vascularis are simultaneously affected in early stages of the disease and the lamination, splitting of the membrane and formation of the "basket weaving" seen at the onset of the disease in the kidney are similar to the ultrastructural alterations characteristic for Alporta9s syndrome. The progressive alteration of the BMs is accompanied by irregularity in the distribution of the collagen IV subunits and by an accumulation of the laminin B2(gamma1) in the inner ear and B(beta1) in the kidney. Since Mpv17 protein contributes to ROS homeostasis, further studies are necessary to elucidate downstream signaling molecules activated by ROS. These studies explain the cellular responses to missing Mpv17-protein, such as accumulation of the extracellular matrix, degeneration, and apoptosis in the inner ear.

Deafness and cochlear fibrocyte alterations in mice deficient for the inner ear protein otospiralin

In the cochlea, the mammalian auditory organ, fibrocytes of the mesenchymal nonsensory regions play important roles in cochlear physiology, including the maintenance of ionic and hydric components in the endolymph. Occurrence of human deafness in fibrocyte alterations underlines their critical roles in auditory function. We recently described a novel gene, Otos, which encodes otospiralin, a small protein of unknown function that is produced by the fibrocytes of the cochlea and vestibule. We now have generated mice with deletion of Otos and found that they show moderate deafness, with no frequency predominance. Histopathology revealed a degeneration of type II and IV fibrocytes, while hair cells and stria vascularis appeared normal. Together, these findings suggest that impairment of fibrocytes caused by the loss in otospiralin leads to abnormal cochlear physiology and auditory function. This moderate dysfunction may predispose to age-related hearing loss.

An emilin family extracellular matrix protein identified in the cochlear basilar membrane

The precise movement of the cochlear basilar membrane (BM) stimulates the sensory hair cells during auditory transduction. However, the molecular composition of the BM that confers its specialized properties of support and elasticity is poorly understood. A differential screen of cochlear RNA from deaf mice lacking thyroid hormone receptor beta was used to identify a sequence encoding a secreted protein, which is abundant in the BM and is expressed at low levels in the heart, lung, and brain. The protein possesses several domains for protein interactions and is related to emilin (elastin microfibril interface-located protein) previously isolated from aorta. This cochlear emilin-2 mRNA is expressed in the tympanic border cells underlying the BM and an antibody detected protein in the extracellular matrix surrounding the collagenous fibers in the BM. These results identify emilin-2 as a major BM component and suggest that it contributes to the developmental assembly or function of the BM.

Immunolabeling type II collagen in the basilar membrane, a pre-embedding approach

This paper describes the development of a protocol that can be used to detect collagen II in the healthy adult basilar membrane (BM) at the electron microscopic level. This protocol required aggressive epitope exposure techniques to break the crosslinks that bind the collagen molecules tightly into fibrils and to remove a dense mat of ground substance that surrounds the fibrils. On the other hand, the steps had to be carefully controlled to preserve BM ultrastructure and the collagen II epitopes that are typically labile. These requirements were satisfied by introducing a targeted crosslink breakage method and by regulating the duration of epitope exposure based on changes in tissue appearance observed with differential interference contrast microscopy. High levels of immunolabeling were achieved by substituting tissue preservation techniques for most or all of fixation; this was important because fixation reduces antigenicity directly and impedes epitope exposure. When these techniques were combined with more traditional trypsin and pepsin treatments, the result was dense immunolabeling and preservation of ultrastructure that allowed accurate localization of the immunolabeling. This pre-embedding immunoelectron microscopic method is the first to be carried out on the BM and may be adaptable to future studies of the BM as well as other tissues with similar molecular composition.

The presence and arrangement of type II collagen in the basilar membrane

Previous studies demonstrating the presence of collagen II in the basilar membrane have used a biochemical approach or have used immunohistochemistry at the light microscopic level. In this investigation both the presence and arrangement of collagen II were demonstrated at the ultrastructural level using pre- and post-embedding immunoelectron microscopy. Labeling was dependent on the development of protocols to expose epitopes while maintaining identifiable ultrastructure. Both positive and negative controls indicate that the labeling was specific for collagen II. Collagen II was detected in the fibrous sheet of the pars tecta and in the two fibrous layers of the pars pectinata. It was detected in situ and on isolated individual 10-12 nm fibrils. The presence of collagen II in all the fibrous layers of the basilar membrane places constraints on the biomechanical properties of this important structure.

Structure of outer hair cell stereocilia side and attachment links in the chinchilla cochlea

The structure and symmetry of chinchilla outer hair cell (OHC) stereocilia side and attachment links were investigated by transmission electron microscopy using tannic acid and Cuprolinic blue histochemical procedures. The side links run laterally between and across the rows of the stereocilia and connect the stereocilia together within the bundle. Attachment links form a crown-like array around the tips of only the tallest OHC stereocilia and attach these stereocilia to the Type B fibrils of the tectorial membrane. Computer averaging of the side links from tannic acid-treated tissues showed a central dense region of the link between adjacent stereocilia and a smaller dense portion at the plasma membrane end of the link. Computer averaging of Cuprolinic blue-treated tissues showed low electron density of the central region of the link, and the plasma membrane ends of the link were electron dense. After tannic acid treatment, the attachment links showed a diffused radial distribution around the tips of the tallest OHC stereocilia. After Cuprolinic blue treatment, the attachment links appeared as electron-dense, membrane-bound granular structures arranged with radial symmetry. The central regions of the side links are reactive to tannic acid. These regions appear to contain neutral and basic residues of proteins and participate in side-by-side association of the side links in regular aggregates. Cuprolinic blue-reactive regions of the side and attachment links appear to contain acidic sulfated residues of glycoproteins or proteoglycans, which may be involved in the attachment of these links to the stereocilium membrane.

Differential expression of alpha 3 and alpha 6 integrins in the developing mouse inner ear

The development of the mammalian inner ear involves a complex series of cell-cell and cell-extracellular matrix interactions. These interactions are likely to be mediated by families of adhesion molecules, including the integrins. We have studied the expression of three integrin subunits known to be expressed on epithelia in a number of tissues (namely, alpha3, alpha6, and beta4) during the development of the murine inner ear. At E10.5, both alpha3 and alpha6 were expressed in the epithelial layers of the otocyst. The expression of alpha6 was concentrated in an anterioventral region of the epithelium and in a proportion of the cells forming the cochlear-vestibular and facial ganglia. By E12.5, alpha6 showed a more restricted expression, confined mainly to the pro-sensory epithelia and the neural processes from the cochlear-vestibular ganglion. In contrast, alpha3 was expressed in epithelia adjacent to the pro-sensory areas. This reciprocal expression pattern was maintained until birth. Between birth and P6, a switch in expression occurred such that alpha3 was upregulated and alpha6 was downregulated in the sensory epithelia of both the auditory and vestibular systems. At this stage, alpha3 was expressed in all the epithelia lining the scala media, thus defining the endolymph compartment. The expression of beta4 was restricted to epithelial/mesenchymal borders throughout the developmental stages studied, suggesting that alpha6 expression observed within the epithelium and neuronal tissue was alpha6beta1. The early expression and changing pattern of alpha3 and alpha6 integrins during development of the mammalian inner ear suggests that they may be involved in the molecular processes that define epithelial boundaries and guide sensory innervation.

Downregulation of otospiralin, a novel inner ear protein, causes hair cell degeneration and deafness

Mesenchymal nonsensory regions of the inner ear are important structures surrounding the neurosensory epithelium that are believed to participate in the ionic homeostasis of the cochlea and vestibule. We report here the discovery of otospiralin, an inner ear-specific protein that is produced by fibrocytes from these regions, including the spiral ligament and spiral limbus in the cochlea and the maculae and semicircular canals in the vestibule. Otospiralin is a novel 6.4 kDa protein of unknown function that shares a protein motif with the gag p30 core shell nucleocapsid protein of type C retroviruses. To evaluate its functional importance, we downregulated otospiralin by cochlear perfusion of antisense oligonucleotides in guinea pigs. This led to a rapid threshold elevation of the compound action potentials and irreversible deafness. Cochlear examination by transmission electron microscopy revealed hair cell loss and degeneration of the organ of Corti. This demonstrates that otospiralin is essential for the survival of the neurosensory epithelium.

Strial marginal cells play a role in basement membrane homeostasis: in vitro and in vivo evidence

The interaction of extracellular matrix and receptors plays a role in tissue homeostasis. The thickened strial capillary basement membrane (SCBM) reported in animal models of presbycusis and Alport's syndrome might be secondary to elevated synthesis and/or decreased turnover of specific basement membrane (BM) components. In this study, expression of specific BM proteins, integrin receptors and mediators of matrix turnover in the murine lateral wall were determined using cDNA probes and antibodies. The presence of collagen alpha1 and alpha2(IV) and laminin-8 in the SCBM was verified. The integrin subunits alpha3, alphav and beta1, cell surface receptors for the BM proteins, localized primarily to the SCBM and/or the strial marginal cells as did TIMP-3, a tissue inhibitor of matrix metalloproteinase. The epithelial cell line SV-k1, derived from the lateral wall of the 'immortomouse', showed expression of the same BM proteins as well as demonstrating the presence of markers specific to strial marginal cells, namely Na,K-ATPase alpha1 and beta2 subunits. Thus, the cultured cells are identified as deriving from marginal cells of the stria vascularis. Moreover, these data suggest that a culture system using this marginal cell line will be useful to delineate mechanisms underlying the pathologic accumulation of extracellular matrix in the SCBM.

Proteoglycan arrays in the cochlear basement membrane

Indirect immunofluorescence and transmission electron microscopy were used to investigate the composition and assembly of proteoglycans in the basement membranes of the spiral limbus, basilar membrane, spiral ligament, Reissner's membrane, myelinated nerve fibers, and blood capillaries of the spiral ligament and stria vascularis in the chinchilla cochlea. Four types of basement membrane components: laminin, entactin/nidogen, type IV collagen and heparan sulfate proteoglycans were immunolocalized in all basement membranes in association with heparan sulfate proteoglycans. beta 1 and alpha 1 integrin subunits were also detected along these basement membranes. The concentration of the basement membrane-associated proteins and integrin subunits differed according to the adjacent cell type. Electron microscopy showed that all basement membranes, with exception of those of stria vascularis, consist of two layers: lamina lucida and lamina densa. In the stria vascularis only a homogeneous lamina densa was observed. Cuprolinic blue treatment revealed heterogeneity in the ultrastructure and arrangement of proteoglycans in the cochlear basement membranes. Proteoglycans of the subepithelial basement membrane in the spiral limbus and spiral ligament formed quasi-regular, linear arrays within the lamina lucida, or were located at both sides of the lamina densa in the basilar membrane and Reissner's membrane. In the basement membranes of nerve fibers, and capillaries in the spiral ligament and stria vascularis, proteoglycans were scattered throughout these basement membranes, but showed different concentration and ultrastructural appearance, which may be related to different filtration and mechanical properties. In the basilar membrane, PGs were located above and below the lamina densa. An additional layer of PGs below the lamina densa may function as increased mechanical support of organ of Corti by its interaction with underlying fibrillar collagen layer. In the stria vascularis capillaries, PGs were stained considerably less with Cuprolinic blue and were scattered through the lamina densa of the basement membrane compared to capillaries of spiral ligament. This observation is compatible with a higher permeability of the strial capillaries.

DFNA9 is a progressive audiovestibular dysfunction with a microfibrillar deposit in the inner ear

OBJECTIVES

Several mutations in the COCH gene were recently identified in American and European families with DFNA9, an autosomal dominant progressive sensorineural hearing loss with onset in high frequencies. Our preliminary vestibular studies in one American family indicated progressive vestibular dysfunction. More complete vestibular studies in European families have shown vestibular abnormalities in the affected individuals. Our temporal bone studies on two families with DFNA9 revealed, in addition to neurosensory degeneration, a unique acidophilic deposit in the membranous labyrinths of the affected individuals. The purposes of this study were 1) to further investigate the vestibular abnormalities in members of one American family for the purposes of genotype-phenotype correlation and 2) to investigate the electron microscopic structure of the acidophilic deposit to obtain further insights into the pathogenesis of DFNA9.

STUDY DESIGN

Prospective analysis.

METHODS

Extensive vestibular testing was performed in some unaffected and affected members of a family with DFNA9. One temporal bone was analyzed by electron microscopy of celloidin-embedded tissue.

RESULTS AND CONCLUSIONS

The findings indicate progressive vestibular dysfunction in many of the patients affected with hearing loss. Thus, despite different mutations in the COCH gene, the American and European families manifest auditory and vestibular dysfunction. Electron microscopic analysis shows the spiral ligament to be enriched for a highly branched non-banded microfibrillar substance that is decorated with glycosaminoglycan granules. Additionally, the spiral ligament lacks the 67-nm-thick straight periodically banded bundles of type II collagen that are normally abundant in this structure. A speculative pathogenetic model is proposed for this unique disease and its relationship with other late-onset or adult-onset audiovestibular diseases and Meniere's disease is investigated.